Quantitation of carcinogenic heterocyclic aromatic amines and detection of novel heterocyclic aromatic amines in cooked meats and grill scrapings by HPLC/ESI-MS

Effects of Phenols from Olive Vegetation Water on Mutagenicity and Genotoxicity of Stored-Cooked Beef Patties

This explorative study aimed to assess the mutagenicity and genotoxicity of stored-cooked beef patties formulated with and without phenols (7.00 mg of phenols/80-g patty) extracted from olive vegetation water (OVW), as related to the formation of cholesterol oxidation products (COPs) and heterocyclic amines (HCAs). The patties were packaged in a modified atmosphere, sampled during cold storage (4 °C) for 9 days, and grilled at 200 °C. The genotoxicity was evaluated by the Comet assay. The patty extract was found to be genotoxic on primary peripheral blood mononuclear cells (PBMCs), while no mutagenicity was detected. The addition of OVW phenols significantly decreased the genotoxicity of the patty extract and reduced the total COPs content in stored-cooked patties (4.59 times lower than control); however, it did not affect the content of total HCAs (31.51-36.31 ng/patty) and the revertants' number. Therefore, these results demonstrate that the OVW phenols were able to counteract the formation of genotoxic compounds in stored-cooked beef patties.

Exposure to melamine and its derivatives and aromatic amines among pregnant women in the United States: The ECHO Program

BACKGROUND

Melamine, melamine derivatives, and aromatic amines are nitrogen-containing compounds with known toxicity and widespread commercial uses. Nevertheless, biomonitoring of these chemicals is lacking, particularly during pregnancy, a period of increased susceptibility to adverse health effects.

OBJECTIVES

We aimed to measure melamine, melamine derivatives, and aromatic amine exposure in pregnant women across the United States (U.S.) and evaluate associations with participant and urine sample collection characteristics.

METHODS

We measured 43 analytes, representing 45 chemicals (i.e., melamine, three melamine derivatives, and 41 aromatic amines), in urine from pregnant women in nine diverse ECHO cohorts during 2008-2020 (N = 171). To assess relations with participant and urine sample collection characteristics, we used generalized estimating equations to estimate prevalence ratios (PRs) for analytes dichotomized at the detection limit, % differences (%Δ) for continuous analytes, and 95% confidence intervals. Multivariable models included age, race/ethnicity, marital status, urinary cotinine, and year of sample collection.

RESULTS

Twelve chemicals were detected in >60% of samples, with near ubiquitous detection of cyanuric acid, melamine, aniline, 4,4'-methylenedianiline, and a composite of o-toluidine and m-toluidine (99-100%). In multivariable adjusted models, most chemicals were associated with higher exposures among Hispanic and non-Hispanic Black participants. For example, concentrations of 3,4-dichloroaniline were higher among Hispanic (%Δ: +149, 95% CI: +17, +431) and non-Hispanic Black (%Δ: +136, 95% CI: +35, +311) women compared with non-Hispanic White women. We observed similar results for ammelide, o-/m-toluidine, 4,4'-methylenedianiline, and 4-chloroaniline. Most chemicals were positively associated with urinary cotinine, with strongest associations observed for o-/m-toluidine (%Δ: +23; 95% CI: +16, +31) and 3,4-dichloroaniline (%Δ: +25; 95% CI: +17, +33). Some chemicals exhibited annual trends (e.g., %Δ in melamine per year: -11; 95% CI: -19, -1) or time of day, seasonal, and geographic variability.

DISCUSSION

Exposure to melamine, cyanuric acid, and some aromatic amines was ubiquitous in this first investigation of these analytes in pregnant women. Future research should expand biomonitoring, identify sources of exposure disparities by race/ethnicity, and evaluate potential adverse health effects.

Formation of Carcinogens in Processed Meat and Its Measurement with the Usage of Artificial Digestion—A Review

Meat is a rich source of various nutrients. However, it needs processing before consumption, what in turn generates formation of carcinogenic compounds, i.a., polycyclic aromatic hydrocarbons (PAH), nitrosamines (NOCs), and the most mutagenic heterocyclic aromatic amines (HAAs). It was widely found that many factors affect the content of carcinogens in processed meat. However, it has recently been discovered that after digestion free HAAs are released, which are not detectable before enzymatic treatment. It was established that the highest percentage of carcinogens is released in the small intestine and that its amount can be increased up to 6.6-fold. The change in free HAAs content in analyzed samples was dependent on many factors such as meat type, doneness, particle size of meat, and the enzyme concentration used for digestion. In turn, introduction of bacteria naturally occurring in the human digestive tract into the model significantly decreases total amount of HAAs. Contrary, the addition of food ingredients rich in polyphenols, fiber, and water (pepper powder, onions, apples) increases free HAAs’ release up to 56.06%. Results suggests that in vitro digestion should be an integral step of sample preparation. Artificial digestion introduced before chromatographic analysis will allow to estimate accurately the content of carcinogens in processed meat.

Heterocyclic Aromatic Amines in Meat: Formation, Isolation, Risk Assessment, and Inhibitory Effect of Plant Extracts

Heterocyclic aromatic amines (HAAs) are potent carcinogenic compounds induced by the Maillard reaction in well-done cooked meats. Free amino acids, protein, creatinine, reducing sugars and nucleosides are major precursors involved in the production of polar and non-polar HAAs. The variety and yield of HAAs are linked with various factors such as meat type, heating time and temperature, cooking method and equipment, fresh meat storage time, raw material and additives, precursor’s presence, water activity, and pH level. For the isolation and identification of HAAs, advanced chromatography and spectroscopy techniques have been employed. These potent mutagens are the etiology of several types of human cancers at the ng/g level and are 100- to 2000-fold stronger than that of aflatoxins and benzopyrene, respectively. This review summarizes previous studies on the formation and types of potent mutagenic and/or carcinogenic HAAs in cooked meats. Furthermore, occurrence, risk assessment, and factors affecting HAA formation are discussed in detail. Additionally, sample extraction procedure and quantification techniques to determine these compounds are analyzed and described. Finally, an overview is presented on the promising strategy to mitigate the risk of HAAs by natural compounds and the effect of plant extracts containing antioxidants to reduce or inhibit the formation of these carcinogenic substances in cooked meats.

Shrimp as a substantial source of carcinogenic heterocyclic amines

In the present work, fifteen mutagenic/carcinogenic heterocyclicamines (HAs)were studied in cooked Caridean shrimp (pink) and Penaeid shrimp (tiger, white and brown). The cooking methods were used as stir-frying, broiling and steaming under controlled temperature and time, and HAs determination was performed by SPE/UPLC-ESI-MS/MS. HAs 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-Amino-1,6-dimethyl-imidazo[4,5-b]pyridine (DMIP), 1-Methyl-9H-pyrido[3,4-b]indole (Harman) and 9H-pyrido[3,4-b]indole (Norharman) were identified (0.05-22.48 ng/g) in all stir-fried and broiled shrimp, whereas 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) was only found (0.08-0.35 ng/g) in stir-fried shrimp. HAs 2-Amino-3,7,8-trimethyl-imidazo[4,5-f]quinoxaline (7,8-DiMeIQx) and, α-carbolines 2-Amino-9H-pyrido[2,3-b]indole (AαC) and 2-Amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC), γ-carbolines 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-Amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and δ-carbolines 2-Amino-6-methyldipyrido[1,2-α:3́,2́-d]imidazole (Glu-P-1) and 2-Aminodipyrido[1,2-α:3́,2́-d]imidazole (Glu-P-2) were not detected or found below quantification limit. Brown shrimp (stir-fried) appeared to be more contaminated which constitutes total HAs (81.93 ng/g) followed by pink (70.41 ng/g), tiger (53.02 ng/g) and white (33.57 ng/g). Steaming method does not yield any HAs, and the cause might be elucidate that shrimp were not directly in contact with cooking pan or fire which affect the HAs formation. Food precursors (protein, moisture, fat, creatine and glucose) were also measured in raw and cooked shrimp to investigate the influence on HAs formation. Creatine (3.85 mg/g) and glucose (0.43 mg/g) were found at higher concentrations in brown shrimp, generates high amounts of HAs. Our findings have illustrated that the cooking method, shrimp types and precursors are the main contributors to the formation of HAs. The outcomes from this work could be applied to estimate the HAs human intake globally and add to steaming cooking method in such types of food products that diminish the risk of HAs exposure, and thus to get healthier food quality and security.

Inhibitory effects of black cumin on the formation of heterocyclic aromatic amines in meatball

The impact of black cumin usage on some qualitative properties and formation of heterocyclic aromatic amines (HAAs) in meatball production was investigated. It was found that black cumin usage rate, cooking process and temperature had a significant effect (p<0,01) on the water content, pH, and thiobarbituric acid reactive substances (TBARS) values of meatballs. On the other hand, black cumin usage significantly (p<0,01) reduced the water content and cooking loss. The water content and cooking loss of the meatballs decreased with increases in the usage rate. While IQx, IQ, MeIQ, 7,8-DiMeIQx, 4,8-DiMeIQx, AαC, and MeAαC could not be detected in meatballs, varying amounts of MeIQx (up to 1,53 ng/g) and PhIP (up to 1,22 ng/g) were determined. The total amounts of HAAs ranged between non-detected (nd) to 2,75 ng/g. Both the usage rate and cooking temperature had a very significant effect (p<0,01) on the total contents of HAAs. The total amounts of HAAs were decreased in correlation with the increases in the usage rate; the proportion which is increased when the cooking temperature increased as well. Results of the present study suggested that addition of black cumin may have a substantial role in decreasing the TBARS value, cooking loss, and HAA contents during meatball production. Therefore, using of black cumin in meatball production has been suggested.

The effects of different frying oils on the formation of heterocyclic aromatic amines in meatballs and the changes in fatty acid compositions of meatballs and frying oils

BACKGROUND

The effects of different frying oils (sunflower, hazelnut, canola, commercially mixed, corn, riviera olive, and natural extra virgin olive) on the formation of heterocyclic aromatic amines (HCAs) in meatballs, and the changes in fatty acid composition of meatballs and frying oils before and after deep-fat frying, were determined.

RESULTS

Frying oils had a very significant effect (P < 0.01) on fatty acid composition and the total HCA content of meatballs. It was determined, in meat, intermuscular fat, meatballs, and all of the different frying oils, that the most common saturated fatty acids (SFAs) were palmitic acid and stearic acid, the most common monounsaturated fatty acid (MUFA) was oleic acid, and the most common polyunsaturated fatty acid (PUFA) was linoleic acid. Only 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was detected in deep-fat fried meatballs, whereas other HCAs (2-amino-3-methylimidazo[4,5-f]quinoxaline (IQx), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ), 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (7,8-DiMeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-9H-pyrido[2,3-b]indole (AαC) and 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC)) could not be detected. The total amount of HCAs in the meatballs ranged between 30.43 and 43.71 ng g^-1 .

CONCLUSION

The results of the present study showed that MeIQx could be formed in deep-fat fried meatballs with different frying oils. The lowest MeIQx content was found in meatballs fried in hazelnut oil and the highest MeIQx content was found in meatballs fried in commercially mixed oil. © 2018 Society of Chemical Industry.

The effects of different spices and fat types on the formation of heterocyclic aromatic amines in barbecued sucuk

BACKGROUND

Sucuk is one of the popular traditional Turkish meat products. The aim of this research was to evaluate the effects of different spices (clove, 0.2%; cinnamon, 0.5%) and animal fat types (beef fat, tallow, subcutaneous and tail fat) on the formation of heterocyclic aromatic amine (HCA) in barbecued sucuk.

RESULTS

Although 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAαC) could not be detected in the any of the samples, 2-amino-3-methylimidazo[4,5-f]quinoxaline (IQx) (up to 0.54 ng g^-1 ), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) (up to 5.96 ng g^-1 ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) (up to 0.21 ng g^-1 ), 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) (up to 0.34 ng g^-1 ), 2-amino-3,7,8-trimethylimidazo[4,5-f]quinoxaline (7,8-DiMeIQx) (up to 0.32 ng g^-1 ), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx) (up to 0.19 ng g^-1 ), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) (up to 1.94 ng g^-1 ) and 2-amino-9H-pyrido[2,3-b]indole (AαC) (up to 0.98 ng g^-1 ) were found in the barbecued sucuk samples.

CONCLUSION

The results of the current study have shown that HCAs could be formed in barbecued sucuk. Total HCA can be affected by adding different fat types; however, adding clove and cinnamon decreased the total HCA content in the subcutaneous fat group of sucuk samples. © 2017 Society of Chemical Industry.

Inhibitory effect of hawthorn extract on heterocyclic aromatic amine formation in beef and chicken breast meat

This study focused on the inhibitory effect of different levels of hawthorn extract (0, 0.5, and 1%) on the formation of heterocyclic aromatic amines (HAAs) in beef and chicken breast cooked by either pan-cooking or oven-cooking. All meat samples were cooked at three different temperatures (150, 200, and 250°C) and the levels of twelve HAAs were assessed (IQ, IQx, MeIQ, MeIQx, 4,8-DiMeIQx, 7,8-DiMeIQx, PhIP, harman, norharman, AαC, MeAαC, and Trp-P-2). Varying levels of IQ (up to 4.47ng/g), IQx (up to 0.69ng/g), MeIQ (up to 0.82ng/g), MeIQx (up to 1.01ng/g), 4,8-DiMeIQx (up to 0.10ng/g), 7,8-DiMeIQx (up to 0.23ng/g), PhIP (up to 0.75ng/g), harman (up to 2.15ng/g), norharman (up to 1.08ng/g), AαC (up to 1.86ng/g), MeAαC (up to 0.48ng/g), and Trp-P-2 (up to 12.88ng/g), were detected. Samples cooked at 150°C had very low amounts of HAAs, and the levels of HAAs increased gradually when the cooking temperature rose from 150 to 250°C. The total HAA content in chicken breast and beef ranged between not detectable to 17.60ng/g, and not detectable to 11.38ng/g, respectively. The inhibitory effects of hawthorn extract at 0.5% and 1% on total HAAs levels were found to be 12-100% and 19-97% in chicken breast, respectively, and 42-100% and 20-35% in beef, respectively. This study demonstrated that hawthorn extracts at 0.5% and 1% could mitigate HAA formation, especially at high cooking temperatures.

Good quantification practices of flavours and fragrances by mass spectrometry

Over the past 15 years, chromatographic techniques with mass spectrometric detection have been increasingly used to monitor the rapidly expanded list of regulated flavour and fragrance ingredients. This trend entails a need for good quantification practices suitable for complex media, especially for multi-analytes. In this article, we present experimental precautions needed to perform the analyses and ways to process the data according to the most recent approaches. This notably includes the identification of analytes during their quantification and method validation, when applied to real matrices, based on accuracy profiles. A brief survey of application studies based on such practices is given.This article is part of the themed issue 'Quantitative mass spectrometry'.

Heterocyclic Aromatic Amines in Cooked Meat Products: Causes, Formation, Occurrence, and Risk Assessment

Meat products are sources of protein with high biological value and an essential source of other nutrients, such as vitamins and minerals. Heating processes cause food to become more appetizing with changes in texture, appearance, flavor, and chemical properties by the altering of protein structure and other ingredients. During heat treatment, heterocyclic aromatic amines (HAAs), potent mutagens/carcinogens, are formed due to the Maillard reaction. The HAAs are classified in at least 2 groups: thermic HAAs (100 to 300 °C) and pyrolytic HAAs (>300 °C). This review focuses on the parameters and precursors which affect the formation of HAAs: preparation, such as the marinating of meat, and cooking methods, including temperature, duration, and heat transfer, as well as levels of precursors. Additionally, factors are described subject to pH, and the type of meat and ingredients, such as added antioxidants, types of carbohydrates and amino acids, ions, fat, and other substances inhibiting or enhancing the formation of HAAs. An overview of the different analytical methods available is shown to determine the HAAs, including their preparation to clean up the sample prior to extraction. Epidemiological results and human daily intake of HAAs obtained from questionnaires show a relationship between the preference for very well-done meat products with increased HAA levels and an enhanced risk of the incidence of cancer, besides other carcinogens in the diet. The metabolic pathway of HAAs is governed by the activity of several enzymes leading to the formation of DNA adducts or HAA excretion and genetic sensitivity of individuals to the impact of HAAs on human cancer risk.

Heterocyclic aromatic amines and their contribution to the bacterial mutagenicity of the particulate phase of cigarette smoke

Heterocyclic aromatic amines (HAAs) rank among the strongest known mutagens. Approximately 30 HAAs have been found in cooked foods (broiled, fried, and grilled) and several HAAs have been characterized as animal carcinogens. Nine HAAs have also been reported to be constituents of cigarette smoke (CS) raising concerns that HAAs might contribute significantly to the known carcinogenicity of CS. As HAAs are found predominantly in the total particulate matter (TPM) of CS, an improved method for the quantification of HAAs in TPM is reported allowing detection and quantification of 8 HAAs in a single run. The mutagenic potency of these HAAs and that of TPM from the reference cigarette 2R4F was determined in the Salmonella Reverse Mutation Assay (Ames assay) with tester strain TA98 and a metabolic activation system. The 8 HAAs, when applied together in the Ames assay, showed a clear sub-additive response. Likewise, the combination of HAAs and TPM, if at all, gave rise to a slight sub-additive response. In both cases, however, the sub-additive response in the Ames assay was observed at HAA doses that are far above the amounts found in CS. The contribution of the individual HAAs to the total mutagenic activity of TPM was calculated and experimentally confirmed to be approximately 1% of the total mutagenic activity. Thus, HAAs do not contribute significantly to the bacterial in vitro mutagenicity of CS TPM.

Measurement of the Heterocyclic Amines 2-Amino-9H-pyrido[2,3-b]indole and 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in Urine: Effects of Cigarette Smoking

2-Amino-9H-pyrido[2,3-b]indole (AαC) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are carcinogenic heterocyclic aromatic amines (HAAs) formed during the combustion of tobacco and during the high-temperature cooking of meats. Human enzymes biotransform AαC and PhIP into reactive metabolites, which can bind to DNA and lead to mutations. We sought to understand the relative contribution of smoking and diet to the exposure of AαC and PhIP, by determining levels of AαC, its ring-oxidized conjugate 2-amino-9H-pyrido[2,3-b]indole-3-yl sulfate (AαC-3-OSO3H), and PhIP in urine of smokers on a free-choice diet before and after a six week tobacco smoking cessation study. AαC and AαC-3-OSO3H were detected in more than 90% of the urine samples of all subjects during the smoking phase. The geometric mean levels of urinary AαC during the smoking and cessation phases were 24.3 pg/mg creatinine and 3.2 pg/mg creatinine, and the geometric mean levels of AαC-3-OSO3H were 47.3 pg/mg creatinine and 3.7 pg/mg creatinine. These decreases in the mean levels of AαC and AαC-3-OSO3H were, respectively, 87% and 92%, after the cessation of tobacco (P < 0.0007). However, PhIP was detected in <10% of the urine samples, and the exposure to PhIP was not correlated to smoking. Epidemiological studies have reported that smoking is a risk factor for cancer of the liver and gastrointestinal tract. It is noteworthy that AαC is a hepatocellular carcinogen and induces aberrant crypt foci, early biomarkers of colon cancer, in rodents. Our urinary biomarker data demonstrate that tobacco smoking is a significant source of AαC exposure. Further studies are warranted to examine the potential role of AαC as a risk factor for hepatocellular and gastrointestinal cancer in smokers.

Red meat-derived heterocyclic amines increase risk of colon cancer: a population-based case-control study

Formation of mutagenic heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) is one pathway believed to drive the association of colon cancer with meat consumption. Limited data exist on the associations of individual HCAs and PAHs in red or white meat with colon cancer. Analyzing data from a validated meat preparation questionnaire completed by 1062 incident colon cancer cases and 1645 population controls from an ongoing case-control study, risks of colon cancer were estimated using unconditional logistic regression models, comparing the fourth to the first quartile of mutagen estimates derived from a CHARRED based food frequency questionnaire. Total dietary intake of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) [adjusted odds ratio (aOR) = 1.87, 95% confidence interval (CI) = 1.44-2.44, P(trend) < 0.0001], 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx) (aOR = 1.68, 95% CI = 1.29-2.17, P(trend) = 0.001) and meat-derived mutagenic activity (aOR = 1.77, 95% CI = 1.36-2.30, P(trend) < 0.0001) were statistically significantly associated with colon cancer risk. Meat type specific analyses revealed statistically significant associations for red meat-derived MeIQx, DiMeIQx, and mutagenic activity but not for the same mutagens derived from white meat. Our study adds evidence supporting red meat-derived, but not white-meat derived HCAs and PAHs, as an important pathway for environmental colon cancer carcinogenesis.

Cytochrome P450-mediated metabolism and DNA binding of 2-amino-1,7-dimethylimidazo[4,5-g]quinoxaline and its carcinogenic isomer 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in mice

2-Amino-1,7-dimethylimidazo[4,5-g]quinoxaline (MeIgQx) is a recently discovered heterocyclic aromatic amine (HAA) that is formed during the cooking of meats. MeIgQx is an isomer of 2-amino-3,8-dimethylmidazo[4,5-f]quinoxaline (MeIQx), a rodent carcinogen and possible human carcinogen that also occurs in cooked meats. MeIgQx is a bacterial mutagen, but knowledge about its metabolism and carcinogenic potential is lacking. Metabolism studies on MeIgQx and MeIQx were conducted with human and mouse liver microsomes, and recombinant human P450s. DNA binding studies were also investigated in mice to ascertain the genotoxic potential of MeIgQx in comparison to MeIQx. Both HAAs underwent comparable rates of N-oxidation to form genotoxic N-hydroxylated metabolites with mouse liver microsomes (0.2-0.3 nmol/min/mg protein). The rate of N-oxidation of MeIQx was 4-fold greater than the rate of N-oxidation of MeIgQx with human liver microsomes (1.7 vs 0.4 nmol/min/mg protein). The rate of N-oxidation, by recombinant human P450 1A2, was comparable for both substrates (6 pmol/min/pmol P450 1A2). MeIgQx also underwent N-oxidation by human P450s 1A1 and 1B1 at appreciable rates, whereas MeIQx was poorly metabolized by these P450s. The potential of MeIgQx and MeIQx to form DNA adducts was assessed in female C57BL/6 mice given [(14)C]-MeIgQx (10 μCi, 9.68 mg/kg body wt) or [(14)C]-MeIQx (10 μCi, 2.13 mg/kg body wt). DNA adduct formation in the liver, pancreas, and colorectum was measured by accelerator mass spectrometry at 4, 24, or 48 h post-treatment. Variable levels of adducts were detected in all organs. The adduct levels were similar for both HAAs, when adjusted for dose, and ranged from 1 to 600 adducts per 10(7) nucleotides per mg/kg dose. Thus, MeIgQx undergoes metabolic activation and binds to DNA at levels that are comparable to MeIQx. Given the high amounts of MeIgQx formed in cooked meats, further investigations are warranted to assess the carcinogenic potential of this HAA.

The C8-2'-deoxyguanosine adduct of 2-amino-3-methylimidazo[1,2-d]naphthalene, a carbocyclic analogue of the potent mutagen 2-amino-3-methylimidazo[4,5-f]quinoline, is a block to replication in vitro

2-Amino-3-methylimidazo[1,2-d]naphthalene (cIQ) is a carbocyclic analogue of the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in which a naphthalene ring system replaces the quinoline unit of IQ. The activity of cIQ in Ames Salmonella typhimurium tester strain TA98 is known to be 4-5 orders of magnitude lower than IQ. cIQ undergoes efficient bioactivation with rat liver microsomes. The C8-dGuo adduct was formed when calf thymus DNA was treated with the N-hydroxy-cIQ metabolite and either acetic anhydride or extracts from cells that overexpress N-acetyl transferase (NAT). These studies indicate that bioactivation, the stability of the N-hydroxylamine ester, and the reactivity of the nitrenium ion with DNA of cIQ are similar to IQ and that none of these factors account for the differences in mutagenic potency of these analogues in Ames assays. Oligonucleotides were synthesized that contain the C8-dGuo adduct of cIQ in the frameshift-prone CG-dinucleotide repeat unit of the NarI recognition sequence. We have examined the in vitro translesion synthesis of this adduct and have found it to be a strong replication block to Escherichia coli DNA polymerase I, Klenow fragment exo(-) (Kf(-)), E. coli DNA polymerase II exo(-) (pol II(-)), and Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4). Previous studies by Fuchs and co-workers identified E. coli pol II as the polymerase responsible for two-base deletions of the C8-dGuo adduct of N-acetyl-2-aminofluorene in the NarI sequence. Our observation that pol II is strongly inhibited by the C8-dGuo adduct of cIQ suggests that one of the other SOS inducible polymerases (E. coli pol IV or pol V) is required for its bypass, and this accounts for the greatly attenuated mutagenicity in the Ames assays as compared with IQ.

The impact of NAT2 acetylator genotype on mutagenesis and DNA adducts from 2-amino-9H-pyrido[2,3-b]indole

2-amino-9H-pyrido[2,3-b]indole (AalphaC) is a carcinogenic heterocyclic aromatic amine (HAA) that is produced in high quantities in tobacco smoke and that also forms in charred meats. The bioactivation of AalphaC occurs by cytochrome P450-mediated (P450 1A2) N-oxidation of the exocyclic amine group, to form 2-hydroxyamino-9H-pyrido[2,3-b]indole (HONH-AalphaC). The HONH-AalphaC metabolite can then undergo further activation by phase II enzymes to form the penultimate ester species, which bind to DNA. Some epidemiological studies suggest a role for NAT2 genetic polymorphisms in human susceptibilities to various cancers from tobacco smoke and from consumption of well-done meats, where the exposures to AalphaC can be substantial. In this investigation, we have measured the genotoxicity of AalphaC in nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human P450 1A2 and either the NAT2*4 (rapid, wild-type acetylator) or the NAT2*5B (the most common slow acetylator) allele, to determine the role of NAT2 phenotype in the biological effects of AalphaC. Mutations at the hypoxanthine phosphoribosyl transferase (hprt) locus were induced in a dose-dependent manner by AalphaC and were found to be highest in cells transfected with P450 1A2 and NAT2*4, followed by cells transfected with P450 1A2 and NAT2*5B. The level of formation of the deoxyguanosine (dG) adduct N-(deoxyguanosin-8-yl)-2-amino-9H-pyrido[2,3-b]indole (dG-C8-AalphaC) paralleled the mutagenic potency in these cell lines. However, AalphaC did not form DNA adducts or induce mutations in untransfected CHO cells or in cells only expressing P450 1A2. These findings clearly demonstrate that NAT2 genetic polymorphism plays a major role in the genotoxic potency of AalphaC.

Carvacrol facilitates heat-induced inactivation of Escherichia coli O157:H7 and inhibits formation of heterocyclic amines in grilled ground beef patties

Heating meat at high temperature and/or for a long time to kill foodborne pathogens increases the formation of potentially carcinogenic heterocyclic amines. To overcome this problem, 1% carvacrol, the main ingredient of oregano oil widely used in salad dressings, was added to ground beef, which was mixed well and then inoculated with Escherichia coli O157:H7. Beef patties were then prepared and heat-treated on a preheated electrical skillet to reach an internal temperature of 65, 70, or 80 degrees C at the cold spot. Samples were enumerated for surviving E. coli O157:H7 population by plating on appropriate media. Heterocyclic amines (MeIQ, MeIQx, and PhIP) were extracted from ground beef using solid phase extraction and analyzed by mass spectrometry. Multiple reaction monitoring (MRM) scan type in positive mode was used to monitor the amines of interest. Compared to controls, the population of E. coli O157:H7 was reduced by 2.5-5 logs. The corresponding highest reductions in the three major amines were MeIQ, 58%; MeIQx, 72%; and PhIP, 78%. The results show that carvacrol concurrently reduced E. coli O157:H7 and amines in a widely consumed meat product. Possible mechanisms of the beneficial effects and dietary significance of the results are discussed.

Quantitation of 13 heterocyclic aromatic amines in cooked beef, pork, and chicken by liquid chromatography-electrospray ionization/tandem mass spectrometry

The concentrations of heterocyclic aromatic amines (HAAs) were determined, by liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-ESI-MS/MS), in 26 samples of beef, pork, and chicken cooked to various levels of doneness. The HAAs identified were 2-amino-3-methylimidazo[4,5- f]quinoline, 2-amino-1-methylimidazo[4,5- b]quinoline, 2-amino-1-methylimidazo[4,5- g]quinoxaline (I gQx), 2-amino-3-methylimidazo[4,5- f]quinoxaline, 2-amino-1,7-dimethylimidazo[4,5- g]quinoxaline (7-MeI gQx), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline, 2-amino-1,6-dimethyl-furo[3,2- e]imidazo[4,5- b]pyridine, 2-amino-1,6,7-trimethylimidazo[4,5- g]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5- f]quinoxaline, 2-amino-1,7,9-trimethylimidazo[4,5- g]quinoxaline, 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-9 H-pyrido[2,3- b]indole, and 2-amino-3-methyl-9 H-pyrido[2,3- b]indole. The concentrations of these compounds ranged from <0.03 to 305 parts per billion (micrograms per kilogram). PhIP was the most abundant HAA formed in very well done barbecued chicken (up to 305 microg/kg), broiled bacon (16 microg/kg), and pan-fried bacon (4.9 microg/kg). 7-MeI gQx was the most abundant HAA formed in very well done pan-fried beef and steak, and in beef gravy, at concentrations up to 30 microg/kg. Several other linear tricyclic ring HAAs containing the I gQx skeleton are formed at concentrations in cooked meats that are relatively high in comparison to the concentrations of their angular tricyclic ring isomers, the latter of which are known experimental animal carcinogens and potential human carcinogens. The toxicological properties of these recently discovered I gQx derivatives warrant further investigation and assessment.